Double upgrades are very rare. I have had one as an op-up in 2006, I think. I didn't ask for it, it was obviously given for operational reasons only.

Each time, did you actually ask for a further upgrade, knowing you had already secured one? If so, maybe it was also granted for operational reasons.

I have had overly chatty FAs openly discussing the behaviour of unnamed F passengers, stipulating that they were "only on award tickets". So despite the doubters here, it's obvious to me that the information is available to them, for any upgrading or award ticketed passengers.

Anyway what the hell does it matter whether or not they know?